CVE-2026-63939

Guest-to-host memory corruption via undersized scratch length

Published Jul 19, 2026 · Updated Jul 19, 2026

Buffer overflow in Linux KVM SEV-SNP allows guest OS users to corrupt host kernel memory via a crafted PSC VMGEXIT request. The GHCB scratch-area setup treats the PSC header's minimum input length as the area's full capacity instead of deriving the remaining length from the guest pointer to the end of the shared buffer. Code execution in an SEV-SNP guest is required; crafted indices then drive out-of-bounds host reads and writes, memory corruption, and kernel panics.

CVSS severity9.3
Critical
EPSS probability0.19%
Next 30 days · Sep 17, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Buffer overflow in Linux KVM SEV-SNP allows guest OS users to corrupt host kernel memory via a crafted PSC VMGEXIT request. The GHCB scratch-area setup treats the PSC header's minimum input length as the area's full capacity instead of deriving the remaining length from the guest pointer to the end of the shared buffer. Code execution in an SEV-SNP guest is required; crafted indices then drive out-of-bounds host reads and writes, memory corruption, and kernel panics.

The record

CVE
CVE-2026-63939
Published
Jul 19, 2026
Updated
Jul 19, 2026
Vendor
The Linux Kernel Organization
Product
Linux Kernel
Classifications
T1068, T1611
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 19, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 19, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=6.11
  2. Affected versionversion=9b54e248d2644be71cb394eb85f31ad99e023a05 <5867d7e202e09f037cefe77f7af4413c7c0fa088
  3. Affected versionversion=9b54e248d2644be71cb394eb85f31ad99e023a05 <6644565527c4c5f507088b1c9ddf72de47790b68
  4. Affected versionversion=9b54e248d2644be71cb394eb85f31ad99e023a05 <6ca9400d36005ffdca25f80186bea781c7e1dc4c
  5. Affected versionversion=9b54e248d2644be71cb394eb85f31ad99e023a05 <9f0a9e780f02c02d025a190f1885e1d1d73b87bd

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

The Linux Kernel Organization · Linux Kernelversion=6.11; version=9b54e248d2644be71cb394eb85f31ad99e023a05 <5867d7e202e09f037cefe77f7af4413c7c0fa088; version=9b54e248d2644be71cb394eb85f31ad99e023a05 <6644565527c4c5f507088b1c9ddf72de47790b68; version=9b54e248d2644be71cb394eb85f31ad99e023a05 <6ca9400d36005ffdca25f80186bea781c7e1dc4c; version=9b54e248d2644be71cb394eb85f31ad99e023a05 <9f0a9e780f02c02d025a190f1885e1d1d73b87bd

Published CVSS scores

9.3LinuxCVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 11, 2026Sep 17, 2026
Latest reporting daySep 17, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1068Exploitation for Privilege Escalation
T1611Escape to Host

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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